The result of studies on the infrared spectra of PrxY1-xBa2Cu3O7-δ system superconductors are reported. It is found that the direct result of increasing the Pr content is that most reflectance features become stronger in the whole energy range (including midle infrared and far infrared). The fingureprint phonon of Y atom at 190cm-1 does not shift when the content of Pr changes. This confirm, that the valence of Pr in this system is greater than +3, which is the valence value of Y in YBa2Cu3O7-δ, and should be between +3 and +4. We also found that, after making the assignment of all phonons, the vibration modes whose strengths increase when the content of Pr increases must be the vibration modes in the CuO2 plane or parallel to the CuO2 plane. This case is much similar to the situ ation of decreasing oxygen content in the YBa2Cu3O7-δ system. It is showed that these vibrations in the CuO2 plane are important for the high-Tc superconduccivity.